Growing vyrezub fish in aquaculture 

Vyrezub, a fish from the Black Sea, Azov and Marmara Seas basin, is very rare, but has excellent taste and great prospects for growing vyrezub in aquaculture. Vyrezub can be grown in pasture fish farming in many reservoirs in Russia, Ukraine, and Moldova. Vyrezub fish can become an important component in polyculture and become a bioreclamation agent for water bodies. Vyrezub can be bred in intensive aquaculture in RAS and cages. In this article you will learn what kind of fish the vyrezub is, what are the features of its breeding, as well as a lot of other useful and interesting information, read to the end, it will be interesting!

Content

• Description of vyrezub fish
• Where is vyrezub fish found?
• What does vyrezub fish look like?
• Vyrezub fish in the Red Book
• Features of vyrezub fish as an object of fish farming
• Vyrezub Spawning
• Vyrezub fertility
• How does vyrezub spawn?
• Breeding vyrezub in artificial conditions
• History of captive breeding of vyrezub
• Formation of vyrezub broodstock
• Experience in growing vyrezub in ponds
• Experience in growing vyrezub in polyculture
• Biotechnology of vyrezub farming

 

 

Description of vyrezub fish 

What is a vyrezub? Vyrezub fish, Latin name Rutilus frisii (Nordmann, 1840), is an anadromous and freshwater fish from the vyrezub family. Three subspecies of vyrezub are known, the first subspecies of vyrezub (Rutilus frisii meidingeri) is a purely freshwater form that lives in the lakes of the upper Danube, in Austria the vyrezub is known as the “pearl fish”. In Russia, there are two subspecies of vyrezub: the vyrezub itself (Rutilus frisii frisii) - an anadromous fish that lives in the basins of the Black and Azov Seas, and kutum - a fish subspecies of the vyrezub (Rutilus frisii kutum) - a migratory fish from the southwestern region of the Caspian Sea, Samura, Chickens, Terek. 

The vyrezub is no less important in fish farming than the sawfish, vimba, shemaya, kutum, bream, pike perch, black vyrezub and others.

 

Where is vyrezub fish found?

 

Where does the vyrezub fish live? The habitat of the vyrezub itself is the river basins of the Black and Azov Seas from Eastern Bulgaria to Western Transcaucasia: it lives in the rivers Dniester, Southern Bug, Dnieper and their tributaries, Don, Seversky Donets and other rivers, Lake Paleostomi. Of the tributaries of the Dnieper, the vyrezub is most often found in Styr, less often in Goryn, Pripyat, Iput, Desna, Sula, Psle, Yasolda, Berezina, Svisloch; along the Dnieper itself the vyrezub reaches Smolensk, and along the Desna - to Bryansk. In the Don, the vyrezub is found as far as Voronezh. The anadromous form of fish, the vyrezub, lives and feeds in the lightly salted waters of the Azov and Black Seas. In the Black Sea, the main part of the vyrezub lives in the brackish water area of the northwestern region, in particular in the Dnieper-Bug estuary. From this estuary, the main part of the vyrezub herd goes mainly to the Southern Bug River. The Dnieper includes smaller numbers of vyrezub.

The vyrezub is a fish found on the Caucasian coast. The vyrezub is also found in many rivers of northwestern Georgia, south to the Rioni River and Lake Paleostomi. On the territory of Russia in the mid-twentieth century, the vyrezub was found in eight rivers of the Black Sea coast within the borders of the Krasnodar Territory - Sukko, Durso, Mezyb, Teshebs, Pshada, Shapsho, Nechepsukho. However, it should be noted that the distribution area of the vyrezub is gradually decreasing. Already in 2003, in the Krasnodar Territory, the vyrezub was found only in the Pshada River.

The vyrezub is a fish where it is found in the Sea of Azov. In the Sea of Azov, the vyrezub prefers to live in its eastern and northern parts; it is found in the Taganrog Bay and Lake Limanchik. From the Sea of Azov, vyrezub rise mainly to the Don and Seversky Donets rivers to spawn. In 1984, the vyrezub was found in the Kuban River, where it had not been found before. The migratory form of vyrezub enters rivers twice: in spring and autumn. The spring movement of the spring form of vyrezub begins with the opening of rivers in March. From the second half of October, the autumn migration of vyrezub begins, and the autumn migration is stronger than the spring one. The winter form goes to the river before freeze-up and overwinters in the river in pits. Vyrezub spawn in April-May in the middle reaches of rivers in areas with clear water, fast currents and rocky bottoms. Most often these are rifts and dams. Vyrezub do not spawn in the lower reaches.

Currently, the migratory form, which rose high along rivers to spawn, has greatly reduced its numbers. Only finds of a residential form in the upper reaches of the Dnieper and Don are reliably known.

Where does the vyrezub fish live without access to the sea. Above dams, vyrezub are able to organize landlocked populations. Such populations were noted in the upper section of the Dniester; in Belarus, small residential forms formed in the rivers of the Dnieper basin.

 

 

What does vyrezub fish look like? 

What does a vyrezub fish look like? The vyrezub can reach 12 years of age; the body length of the vyrezub reaches up to 70 cm and the weight is about 8 kg. The body of the vyrezub is elongated, not very flattened laterally. The mouth is terminal, semi-inferior or lower, the upper jaw protrudes slightly above the lower. The snout is blunt, rounded. The forehead is wide and convex. The back of the fish is dark, the sides are light silver, the belly is white; the dorsal and caudal fins are dark in color, the remaining fins are grayish.

The vyrezub has the following body proportions: the length of the head is on average 1/5 of the length of the body, the lengths of both blades of the caudal fin are close to it, and are equal to each other. The height of the dorsal fin is close to the length of the pectorals, and the base of the anal fin is close to its height.

There are 53-68 scales in the lateral line. There are 7-12 gill rakers, according to other sources – 9-10. Vertebrae 41- 44, usually 43. Pharyngeal teeth are single-row, powerful, short, usually 6-5, rarely 6-6 or 5-5.

 

Vyrezub fish in the Red Book

 

The vyrezub fish is one of the species that has suffered the most from human activity. Under the influence of such factors as the small number of spawners, the lack or poor condition of spawning grounds, sharp fluctuations in water levels during the spawning period, as well as other unfavorable hydrological indicators during the period of egg incubation and in the early stages of juvenile development, the number of vyrezub has decreased.

By the middle of the 20th century, this fish completely lost its commercial importance. The number of vyrezub throughout its range has decreased so much that the vyrezub was included in the Red Books of Russia, Ukraine, Moldova, Belarus, as well as in the IUCN-96 International Conservation List.

 

Features of vyrezub fish as an object of fish farming 

 

Vyrezub has good tasty meat, which makes it a gourmet product of a high price category, which can be comparable to the price of trout and sturgeon.

An important feature of growing vyrezub in aquaculture is the ability to consume shellfish, which makes it a promising object for growing in polyculture, where it will occupy a food niche that is not used.

The vyrezub actively consumes mollusks, including zebra mussels, even at temperatures of 8-12 C. The vyrezub grinds the shells and swallows them along with the body of the mollusks. However, the vyrezub can successfully eat grain and artificial feed, which makes it easier to grow in fish farming.

In an adult vyrezub, the average annual weight gain can reach an average of more than 500 g. In terms of the comparative productivity coefficient, the vyrezub can surpass most vyrezub fish of the Azov, Aral and Caspian seas, including vyrezub.

There are few mollusc eaters in reservoirs, and compared to black vyrezub, the vyrezub has such an important advantage as the ability to naturally reproduce in the conditions of reservoirs in the European part of Russia, Ukraine, Moldova, and Belarus, creating local herds. This is all the more important because currently shellfish represent a significant biomass food resource in most reservoirs, which is very poorly used by most fish species. In large reservoirs, 80-90% of zoobenthos consists of mollusks. Therefore, in pasture fish farming, by introducing vyrezub into reservoirs, taking into account its ability to eat mainly zebra mussels, the commercial fish productivity of reservoirs can be significantly increased.

Vyrezub Spawning

 

Vyrezub fertility 

The average age of vyrezub maturation is 5 years. The vyrezub is a highly fertile fish; it is second in fertility among vyrezub fish only to vyrezub, tench, crucian vyrezub and bream. The fecundity of the vyrezub ranges from 89 to 256 thousand eggs, with an average fecundity of 138 thousand eggs, which is more than twice the fecundity of the cutum. 1 g of vyrezub caviar contains an average of 370 eggs. In fish farming, the working fertility of female vyrezub averaged 80 thousand eggs (60-116 thousand).

How does vyrezub spawn?

 

When does vyrezub spawn? Vyrezub spawn in April–May, in areas with cold water and in the current, when vyrezub eggs stick to the rocks. When the water warms up to 9-10 ° C, the males go to the rifts to the spawning grounds in the upper reaches of the rivers in order to prepare places for spawning. When entering rivers, male vyrezub are covered with epithelial tubercles, with which they rub against stones, cleaning the stones from eggs of other fish, mucus, algae, etc. By this time, female vyrezub enter holes located near the spawning sites. Vyrezub spawning begins at a water temperature of 8-14 °C. A female vyrezub, accompanied by two or three males, rubs against the rocks and spawns. Vyrezub spawn only once. The largest individuals spawn first, then the smaller individuals begin to spawn. Vyrezub spawning lasts about two to three weeks, depending on the water temperature and its changes. 

During spawning, vyrezub are very sensitive to environmental conditions. It is negatively affected by such factors as water turbidity caused by wastewater discharge. During this period, sudden changes in temperature are especially dangerous. In the presence of such factors, the vyrezub stops spawning and rolls into holes downstream.

Vyrezub growth rate 

How fast does the vyrezub grow? Vyrezub larvae in the early stages of development stay on stretches, near spawning grounds. At the age of 4-5 months, juvenile vyrezub migrate downstream. Recently, there have often been cases where juvenile vyrezub remain in the river for 1-2 years. In the first year of life, the vyrezub reaches a weight of up to 5 g, a two-year-old - up to 60-80 g, a three-year-old - up to 300-500 g.

The vyrezub grows relatively quickly; it is important that, provided that the vyrezub is grown in ponds and RAS, it is not much inferior to the growth of the vyrezub in natural conditions.

 

Breeding vyrezub in artificial conditions

History of captive breeding of vyrezub 

There is positive experience in rearing juvenile vyrezub in floating cages. Of the 34 thousand larvae, 15 thousand fry were raised from April 25 to July 13. The yield was 44%. It should be noted that the juveniles were of low quality, since at the age of 73 days they had an average length of 31.4 mm and a weight of 115 mg. The obtained result showed that fry of rheophilic fish such as vyrezub survive quite well in cage conditions with weak flow and high crowding.

There is positive experience in growing vyrezub in rice paddies in Ukraine, on the banks of the Southern Bug. The checks were poured at the end of May, so the fry, 45 thousand in number, were kept in three floating cages for almost a month before pouring. The fry were fed with daphnia; in the absence of natural food supply, corn flour was used. Then the fry were towed in Ses-Grin devices to the rice paddies, where the fry fed on zooplankton, which, in terms of qualitative composition, was good, but its quantity was clearly insufficient. In checks, juvenile vyrezub were raised until September 30. The yield ranged from 21.3 (in checks with high planting density) to 60.5% (in checks with low planting density).

Despite high temperature changes (the difference between morning and afternoon was up to 14°C), insufficient nutrition and heavy overgrowth of rice stalks, algae and weeds, the reared juveniles were strong and were capable of producing a high commercial return. In the checks, the juveniles ate mixed food, in which, depending on age, animals or plants predominated.

Formation of vyrezub broodstock 

 

The first attempts at artificial breeding of vyrezub and subsequent release of juvenile vyrezub into rivers were based on the use of spawners that were caught from rivers during spawning. At present, it is more expedient to form a broodstock of vyrezub and organize our own production of planting material for stocking natural reservoirs and commercial cultivation. But the history of vyrezub breeding and growing it in aquaculture knows many successful and not so successful experiences.

More modern calculations show that with a fishery return rate of 3%, to ensure an annual catch of 240 tons, it is necessary to release 4 million fry annually, which will require about 120 females and 85 males. At the same time, a production base is needed for intensive industrial breeding of vyrezub with a total area of nursery ponds of 65-70 hectares, designed for a juvenile yield of 65-70 thousand/ha.

 

Experience in growing vyrezub in ponds

 

To ripen vyrezub spawners, we prepared earthen cages, scattered crushed stone along the bottom in a strip and increased the water flow to 80-100 l/min, bringing the spawners’ keeping conditions closer to those of the river. To speed up the maturation of females, two or three “fluid” males are placed next to them in the fenced off upper part of the cage after a permissive injection.

At a stable water temperature of 14°C and a permissive injection of 8 mg/kg of body weight, 4/5 females mature in 19 hours. Ripe females release eggs in a single portion with light massaging of the abdomen. In total, 3064 g, or 1133.7 thousand eggs, were obtained from 14 females (1 g of vyrezub caviar contains on average 370 eggs). The working fertility of vyrezub females averaged 80 thousand eggs (60-116 thousand).

Degumming of eggs after fertilization was carried out in Weiss apparatus with a milk solution for at least 1.5 hours, incubation and maintenance of free embryos in Yushchenko apparatus with a load of 200 thousand eggs. The duration of incubation at a water temperature of 12-17°C was 11-12 days. The yield of free embryos is 93-88%, the yield of larvae is 90%.

With a stocking density of larvae of 200 thousand pcs./ha and a vyrezub rearing duration of 100-120 days, the mass of fingerlings was 4.6 g, at a higher density - up to 300 thousand pcs. – the growth rate decreased.

The yield of fingerlings weighing at least 4 g from planting larvae was 32%. The productivity of ponds when growing vyrezub in monoculture was 90-100 thousand pieces/ha.

 

Experience in growing vyrezub in polyculture

 

In 2010, I.A. Alimov presented the experience of growing vyrezub fingerlings in polyculture with larvae of silver vyrezub, grass vyrezub and catfish. The fry, grown to an average weight of 24 mg, were brought from the Medveditsky fish factory and planted in a nursery pond in the amount of 2 thousand. The fry were planted in a nursery pond with an area of 0.4 ha. At the same time, along with vyrezub, three-day-old larvae of silver vyrezub and grass vyrezub (50 thousand pieces) and five-day-old larvae of catfish (Silurus glanis) (2.0 thousand pieces) were released into this pond.

After 15 days from the moment of stocking, the juveniles began to be fed with K-111 compound feed.

A unique set of fish species grown in one pond was determined by the task of raising resilient young-of-the-year catfish that can successfully overwinter in the first year of life. The larvae of grass vyrezub and silver vyrezub were used as food.

The rearing of vyrezub fingerlings was purely experimental.

During the period from June to October 2009, the average vyrezub weight reached 10.5 g with a survival rate of 91.8%.

During the growing season, the vyrezub quickly adapted to the consumption of feed and produced good growth.

The vyrezub fingerlings were distinguished by their uniformity. The range from the average value was from 9 to 12 g. The vyrezub tolerated the catch quite well.

Subsequently, in June 2010, the yearlings were planted in the feeding and experimental ponds. Along with vyrezub, crucian vyrezub, as well as three-day-old larvae of catfish and grass vyrezub, were placed in the experimental pond. In the feeding pond, vyrezub were raised together with three-year-old vyrezub, grass vyrezub, catfish and crucian vyrezub. As a result of fishing in October 2010, two-year-old vyrezub in the feeding pond had an average weight of 91 g, and in the experimental pond - 105.4 g, with a survival rate of 79%. At the Medveditsky fish factory, where the experimental fish was obtained, two-year-old vyrezub by that time had reached 130 g with a relatively good survival rate. Thus, juveniles and two-year-old vyrezub can be raised in polyculture conditions.

Biotechnology of vyrezub farming

 

In general, researchers indicate that the biotechnology of growing vyrezub is very close to the biotechnology of growing its closest relatives - vimba and kutum and therefore use them in practice.

It is indicated that ponds with an area of 3-5 hectares are used for rearing juveniles. Ponds must be drainage with independent water supply and discharge. They must have a systematic supply of water to cover losses due to evaporation and filtration. The depth of the ponds is from 0.5 to 1.8 m (average - 1 m). The time for draining the pond should not exceed 2 days. 2 days before filling the ponds with water, their beds and dividing dams must be mowed. Mown and dried vegetation is stacked near the pond collectors in an amount of 200-300 kg/ha.

The ponds begin to be filled with water before the larvae are planted in them: 6-8 days before - at a water temperature of 10-12°C, 3-5 days before - at a temperature of 14-16°C and above. The initial water level in the ponds is maintained for 7-10 days not higher than 20-30 cm, which contributes to good heating of the water and the rapid development of ciliates, algae and rotifers, which are the food of the larvae in the first days of life in the ponds, as well as a higher concentration of feed on unit volume of water.

The larvae are counted in the hatchery workshop according to the standard method, placed in baths or plastic bags and transported to ponds with a prepared food supply. When grown in monoculture, the density of planting larvae in ponds is 150-300 thousand pcs./ha. After stocking the ponds with fish, the water level in them is increased within 10 days and brought to the design level.

As the larvae grow, the composition of their food ration changes. They begin to consume, along with small and larger planktonic organisms - juvenile crustaceans. The grown-up juveniles of these fish feed mainly on adult forms of zooplankton.

During the entire period of growing juveniles in ponds, observations are made of the thermal regime, oxygen content in the water and the development of the food supply. The water temperature in the ponds is measured daily at 7, 13 and 19 o'clock. The oxygen content and pH value in the ponds are determined once every 5 days. Water samples are taken in the morning (at 4-5 o'clock).

Organic fertilizers are reapplied to the pond after 30 days, since their effect on increasing the number and biomass of zooplankton ceases after 35 days. The repeated dose of green fertilizers applied to ponds is 200 kg/ha. This allows you to maintain a high food supply in the ponds until the end of the fry rearing period. Throughout the entire period of growing the fry, you need to monitor its nutrition and growth. For this purpose, a control fishery of the pond is carried out once a week. The mortality of juveniles during the period of rearing in ponds is 15-30%.

The juveniles are raised in ponds for 2-2.5 months until they weigh 1 g, after which they are counted and released into natural reservoirs.